This invention is for a threaded fastener embedded in a plastic material of a utility box for holding bolts with a large applied torque to fasten a corner on the box.
In recent years, vaults or boxes for protecting underground permanently installed utility equipment have been constructed from plastics. It has been customary to hold the covers to these boxes in place by simply bolting on the cover, and applying sufficient torque to the bolt to hold the bolt tightly in place. This prevents the bolt from being loosened accidently, or by a curious passer-by, or a mischievious juvenile. Since these boxes protect circuits that are very dangerous and frequently vital in the distribution of utilities, it is readily apparent that a simple system which will provide security and quick repair access is highly desireable. In the past, the torque that could be applied to the bolt fastening the cover of these boxes was limited by the arrangement for holding the nut to, for example, about 25 ft-lbs. torque.
Fasteners made in accordance with this invention have considerably increased the torque which can be applied. For example, fasteners in accordance with this invention have withstood 55 ft-lbs., and, in fact, the bolt will usually shear before the fastener will rotate using the instant invention.
Secondly, prior art threaded fasteners embedded in the plastic have tended to pull out axially due to axial stress when the bolt is threaded through it and tightened. An advantage of the instant invention is to provide much greater resistence to this tendency. Comparable prior fasteners withstood only up to around 600 pounds of axial pull, whereas the instant invention has withstood up to 900 pounds axial pull.
Finally, it has been observed that pressure brought directly upon the plastic in which the fastener is embedded tends to reduce the ability of the plastic to resist rotation and axial pulling of the fastener. The instant invention provides for the fastener to act as a bearing surface, to avoid compression of the embedding plastic upon the torqueing a threaded bolt into place.